"Brew house efficiency is the calculation of the overall efficiency of your brewing system. It takes into consideration the percent of potential grain sugars that are converted in the mash, effectively washed during the latuer and all wort losses in your system. If you do not accurately calculate the brew house efficiency of your brewing system you will find it very difficult, of not impossible, to anticipate the OG of the recipes that you are brewing. Here are some helpful equations to calculate efficiency in your brewing system: The following equations assume 10 pounds of 2-row pale malt in 5 gallons of water, with a mash/lauter efficiency of 75%.